The present invention relates to inspecting glass containers and other containers having transparent or translucent sidewalls, and more particularly to inspecting such containers for forming defects such as "birdswings".
A variety of types of defects are known to occur in glass containers as a result of the forming process. The method and apparatus of the present invention are particulary applicable to the detection of structural irregularities on the inner surface of the container sidewalls. One such defect, known as a "birdswing", is formed when the two sides of the container contact each other during the formation of the parison and prior to blowing the container into its final shape. At this stage the touching of the two walls of the container may cause the hot glass sides to fuse together, so that as the container is blown to its final shape the sides which have touched will move away from each other forming a small thread of glass therebetween, i.e. a "birdswing". A birdswing need not comprise a complete thread between the two inner walls, inasmuch as the thin filament of glass may break rather than stretch during rapid cooling of the article. Inevitably, however, there will be a small conical protruberance from the sidewall directed toward the opposite sidewall.
Various prior art practitioners have sought to detect birdswings and other defects by passing a light beam through the wall of the container. Illustrative patents of this type include U.S. Pat. No. 4,438,492, to W. R. Albers; U.S. Pat. No. 3,662,883, to J. R. Sager; and a series of patents commonly assigned to Inex, Inc. including U.S. Pat. No. 3,886,356 to Gomm et al.; U.S. Pat. No. 3,877,821 to Price et al.; U.S. Pat. No. 3,932,767 to Gomm et al.; and U.S. Pat. No. 3,956,629 to Gomm et al. These systems generally use a solid state television camera or similar electro-optical detection device to scan the glass container, which is illuminated from behind. The birdswing appears as a "dark spot" in the image as the filament and its attachment to the sidewall occlude light passing through the container. This approach encounters a number of serious shortcomings in accuracy and sensitivity. Other defects, such as checks, cracks, blisters, or stones might appear in the wall of the container, also causing dark spots in the image. There is a serious risk of these other types of defects being mistaken for birdswings when in some cases only the latter defect is of concern. Thus, if the detection threshold of these devices is set at a sufficiently low value to discover relatively small birdswings, the system may reject acceptable glassware. In addition, lettering or other patterns embossed on the outer surface of the glassware will also appear as dark spots. If these surface decorations are masked in order to prevent detection, any birdswings appearing thereunder will not be detected.
U.S. Pat. No. 4,249,075 to Lovalenti discloses an alternative apparatus for detection of birdswing defects. In the Lovalenti system a container under inspection is rotated and a laser is directed through the opening defined by its finish, toward the container base. If no birdswing is present, the laser beam will pass through the bottom, but the presence of a birdswing being scanned will cause the laser light to be scattered, and detected by a circumferential protocell array. With reference to page 3, lines 8 et. seq. of the Lovalenti specification, this detection system suffers the shortcoming that the user must accept a tradeoff between the sensitivity of this device to relatively small birdswings as against the portion of the inner container wall which will be effectively scanned.
A variety of prior art references apply a further detection principle to the general task of inspecting glassware for various types of defects, in which the ware is scanned to monitor any light reflected by the defect. Illustrative U.S. patents disclosing apparatus of this nature include:
U.S. Pat. No. 3,328,000: Rottmann PA1 U.S. Pat. No. 3,349,906: Calhoun et al. PA1 U.S. Pat. No. 3,415,370: Husome PA1 U.S. Pat. No. 3,529,167: Calhoun PA1 U.S. Pat. No. 3,601,616: Katsumata PA1 U.S. Pat. No. 3,651,937: Kronseder PA1 U.S. Pat. No. 3,834,429: Schulz PA1 U.S. Pat. No. 3,987,301: O'Conner PA1 U.S. Pat. No. 4,002,823: Van Osterhout PA1 U.S. Pat. No. 4,140,901: Fischer et al. PA1 U.S. Pat. No. 4,165,277: Frewin PA1 U.S. Pat. No. 4,171,481: Mima et al. PA1 U.S. Pat. No. 4,213,042: Beach et al. PA1 U.S. Pat. No. 4,221,961: Peyton PA1 U.S. Pat. No. 4,399,357: Dorf PA1 U.S. Pat. No. 4,424,441: Bieringer et al.
None of the above-listed references disclose an inspection system which would be particularly well suited to provide an accurate and sensitive detection of birdswing defects. U.S. Pat. No. 4,165,277 to Frewin describes a monitoring unit having a plurality of scanning photodiodes with associated phototransistors. The photodiodes are sequentially energized to emit light pulses, illuminating an area of interest of the glassware. Error pulses are generated by phototransistors when a defect is sensed in light reflected from the article. The Frewin apparatus, designed for detection of "in the wall" defects, would not effectively descriminate between birdswings and other defects.
U.S. Pat. No. 4,424,441 to Bieringer et al, discloses photoinspection apparatus in which the container finish is illuminated with diffused light in order to monitor the finish for check-type defects having a horizontal component--an approach obviously unsuitable for detection of birdswings. The apparatus of U.S. Pat. No. 4,399,357 to Dorf et al., which is specially designed for detection of defects such as horizontal checks in the sidewall of a glass container, directs radiant energy into the sidewall of the container from above while the container is rotated. The Dorf system trains a detector device such as a television camera on the outer sidewall to scan the container for light reflected by a horizontal check or similar defect within the sidewall. The Dorf et al. apparatus would not provide sensitive and reliable detection of birdswings and similar forming defects on the interior of the container sidewalls, nor avoid undesired detection of other defects. Inasmuch as it relies on light internally transmitted through the sidewall to detect defects, it is highly vulnerable to various transmission losses.
Accordingly, it is a principal object of the present invention to achieve apparatus for detecting birdswings and like forming defects, in a sensitive and reliable fashion. A related object is to detect an appreciably complete percentage of birdswing defects present in the container, while avoiding signals indicative of other defects such as imperfections within the sidewall. Another related object is to avoid undesired indications of embossed surface decorations on the exterior of the container sidewalls.
An additional object of the invention is to achieve container inspection apparatus which effectively scans the entire inner sidewall of glass containers. This object should be satisfied while providing a high sensitivity for detection of relatively small or partially formed birdswings which may appear as spikes.
A further object of the invention is to design apparatus for detection of birdswings which may be effectively used in tandem with inspection apparatus for other types of defects.
Apparatus for this purpose should be sturdy and reliable, and designed to be effectively operated by relatively unskilled users. Most desirably, these inspection devices should have an inspection capability for a variety of container types--e.g. different wall thicknesses, side wall profiles, glass colorations, etc.